1. Field of the Invention
Embodiments of the present invention relate to the field of timing controllers. More particularly, embodiments of the present invention relate generally to a differential pre-drive circuit exhibiting reduced swing and offset.
2. Related Art
Liquid crystal displays (LCDs) are important to the television market. However, pushing LCDs to the next generation by simply scaling existing LCD monitor panels to wider formats (e.g., 16:9 HDTV) and larger formats is a complicated endeavor. A number of television requirements push beyond conventional state-of-the art monitors. For instance, response time, brightness, contrast, color envelope, color temperature, and progressive scan-and-hold issues require a re-engineering of the monitor solution.
Specifically, LCD televisions bring forward a completely new set of challenges that are broader than simple data signaling issues. The demand for up to HDTV formats (1920×1080) on display sizes beyond 50 inches are problematic. For example, longer transmission distances (due to larger display sizes) and higher data rates (due to larger pixel formats) combine to push clock and data registration beyond stable limits.
In particular, conventional transmitter designs have limited maximum operating frequencies and less than ideal output waveforms exhibiting overshoot and undershoot disturbances. In a pre-drive circuit of conventional transmitter designs, data channels between a timing controller and a column driver are driven by complementary-symmetric metal oxide semiconductor (CMOS) logic. That is, output devices in the transmitter are driven with rail-to-rail CMOS signaling. As a result, this type of pre-drive limits the maximum frequency of the transmitter and correspondingly the data channel. This limitation occurs since it takes time to charge and discharge the channels of the output transistors. In addition, this type of pre-drive creates glitches in the output waveform because the channels of the transistors in the output stage are completely charged and discharged as they leave and re-enter the saturated operating mode. Specifically, as the charge is removed and replaced, glitches appear in the output waveform through capacitive coupling.